Using VM 2.0.24c (and 2.0.26c on dev server), php 5.3 on both. I don't recall seeing this before 2.0.24c (but it's possible I just never noticed it before).
If I add a product to the cart and *quickly* click "show cart" in the modal, about 33-50% of the time the cart is empty. If I go back and add it again, and *quickly* click "show cart" it is almost always added (easiest to reproduce in an incognito tab/window).
Live URL to product that displays this behavior (warning: this is a FUNCTIONING shop!):
http://buddyrest.com/orthopedic-dog-beds
Earlier I turned off all the third-party plug-ins to no effect.
Can anyone else reproduce? Any ideas on where to look? I've double-checked the $live_url, killed alternate versions of jQuery, turned off third-part VM extensions/plugins... not sure where to look next. Is there still a way in VM2 to turn off the AJAX "add to cart" and just POST/GET? Not optimal I know but might be a good stop-gap.
Chris
Have you solved this? I tested your link and could not replicate the problem.
That said, I have a client site experiencing a similar problem, but only among certain users. Because I cannot reproduce the problem on any of my own several computers and browsers, this is very difficult to track down. If you have a moment, would you test this live site to see if you can produce the same add to cart issue you are seeing with your site?
http://markvlab.com
Thanks for any help.